66 



THE SKELETON 



Borders. — The posterior border extends from the body to the spine. By its lateral third it 

 articulates with the petrous portion of the temporal bone, whilst the medial two-thirds form the 

 anterior boundary of the foramen lacerum. The squamosal border is serrated behind and 

 bevelled in front for articulation with the squamous portion of the temporal bone, whilst its 

 upper extremity, or summit, is bevelled on its inner aspect, for the anterior inferior angle of the 

 parietal. Immediately in front of the upper extremity is a rough, triangular, sutural area for 

 the frontal, the sides of which are formed by the upper margins of the superior, anterior, and 

 lateral surfaces respectively. The zygomatic or anterior border separates the orbital and tem- 

 poral surfaces and articulates with the zygomatic, and by its lower angle, in many skulls, also 

 with the maxilla. Below the anterior border is a short horizontal ridge, non-articular, which 

 separates the spheno-maxillary and zygomatic surfaces. Above and medially, where the orbital 

 and cerebral surfaces meet, is the sharp medial border, which forms the lower boundary of the 

 superior orbital fissure, serving for the passage of the third, fourth, three branches of the first 

 division of the fifth, and the sixth cranial nerves, the orbital branch of the middle meningeal 

 arter}', a recurrent branch from the lacrimal artery, some twigs from the cavernous plexus of 

 the sj'mpathetic, and one or two ophthalmic veins. Near the middle of the border is a small 

 tubercle for the origin of the lower head of the lateral rectus muscle. 



The pterygoid processes project downward from the junction of the body and 

 the great wings. Each consists of two plates, one shorter and broader, the lateral 

 pterygoid plate [lamina lateralis], the other longer and narrower, the medial 

 pterygoid plate [lamina medialis]. They are united in front, but diverge behind 

 so as to enclose between them the pterygoid fossa in which lie the internal 'pterygoid 

 and tensor palati muscles. The lateral pterygoid plate is turned a little laterally 

 and by its lateral surface, which looks into the zygomatic fossa, affords attach- 

 ment to the external pterygoid muscle, whilst from its medial surface the internal 

 pterygoid takes origin. 



The posterior border of the lateral pterygoid plate frequently presents one or more bony 

 projections, which represent ossified parts of the pterygo-spinous ligaments, and occasionally 

 one may extend across to the spine and complete the bony boundary of the pterygo- 

 spinous foramen. The medial pterygoid plate is prolonged below into a slender, hook-like or 

 hamular process, smooth on the under aspect for the tendon of the tensor palati, which plays 

 round it. Superiorly, the medial plate extends medially on the under surface of the body, 

 forming the vaginal process, which articulates with the ala of the vomer and the sphenoidal 

 process of the palate. The vaginal process presents, on the under surface,' a small groove 

 which, with the sphenoidal process of the palate, forms the pharyngeal canal for the trans- 

 mission of branches of the spheno-palatine vessels and ganglion. The medial surface of 

 the medial pterygoid plate forms part of the lateral boundary of the nasal fossa, and the 

 lateral surface, the medial boundary of the pterygoid fossa. The posterior border presents 

 superiorly a well-marked prominence, the pterygoid tubercle, above and to the lateral side 

 of which is the posterior orifice of the pterygoid canal. The latter pierces the bone in the 

 sagittal direction at the root of the medial pterygoid plate and transmits the Vidian vessels 

 and nerve. Some distance below the tubercle is a projection, called the processus tubarius, 

 which supports the cartilage of the tuba auditiva (Eustachian tube). From the lower third 

 of the posterior border and from the hamular process, the superior constrictor of the pharynx 

 takes origin, and from the depression known as the scaphoid fossa, situated in the upper part 

 of the recess between the two pterygoid plates, the tensor palati arises. 



Fig. 83. — The Sphenoid at Bihth. 



Pterygoid canal 



Lingula 



In front, the two plates are joined above, but diverge below, leaving a gap — 

 the pterygoid notch — occupied, in the articulated skull, by the pyramidal process 

 of the palate. Sui)eriorly, the}^ form a triangular surface which looks into the 

 pterygo-palatine fossa and i)r('sents the anterior orifice of the pterygoid canal. 

 The anterior border of the medial pterygoid plate articulates with the posterior 

 border of the vertical plate of the palate. 



Blood-supply. — The sphenoid is supplied by brunches of the middle and small meningeal 

 arteries, the (lcc[) temi)oral and other brunches of the internal maxillary artery — viz., the 

 Vidian uiid splicno-p.-iiatine. The body of the bone also receives twigs from the internal carotid. 



Articulations. ^Thc sphenoid articulates with all the bones of the cranium — viz., occipital, 



